Taps and Dies (1 Viewer)

[ozwallaby]

Maybe an older school fitter/turner/toolmaker can help me out....

I have recently been given some quite small taps which have size markings on them.... The original owner passed away some time ago and his daughter gave them to me....here is the quandry.... on the shaft of the taps are various references to their size I presume and the thread count.... ie 10 24 or 8 32.... I new straight away that the thread count for the 2 examples here are 24tpi and 32tpi respectively... but what does the other number refer to... the pilot drill size perhaps and if so... what is a no. 10 or no. 8 drill

Another one of the taps has all of this on a single small tap ( I had to use a magnifying glass to read it) Threadit (the brand I suspect)... 6-32.... Made in USA.... use drill no. 36..... This tap is less than 1/8 in diameter.... What is drill no. 36?... I do realize it is a reference to the pilot drill size but what size is no. 36....


Another one has .222 22.... so 22tpi and I imagine pilot hole 222 thou....

thnx in advance

 

[ferg]

Those are inch sized tools. '6', '8' or '10' refers to the screw/bolt size - non metric. Drill bits come in number sizes as well as fractional sizes. Most number drill index sets come in '0' to '60', the larger the number the smaller the bit. I don't know about the '.222' item.

My last job we had #80 taps for some reeeaaaaly tiny adjustment screws on HUD cameras.

 

[ozwallaby]

So it's a number 6 thread or a number 8 thread etc, I get that part.... but these numbers must be an actual measured size surely... like a number 6 is equal to 118/985ths..... or something silly like that....

 

[ferg]

The thread is the '24' or '32', as in threads per inch. Similar to pitch on metric threads. The first number is the fastener major diameter. Yes they conform to a decimal equivalent but I don't know those values.

 

[ozwallaby]

Thnx @ferg.... I've tracked down some info on a sight called engineersedge.com...... it gives what appears to be all the equivalent measured sizes for the lettered and numbered drill sizes.... ya sure can drill some small holes if you want.

 

[PAToyota]

I have recently been given some quite small taps which have size markings on them.... The original owner passed away some time ago and his daughter gave them to me....here is the quandry.... on the shaft of the taps are various references to their size I presume and the thread count.... ie 10 24 or 8 32.... I new straight away that the thread count for the 2 examples here are 24tpi and 32tpi respectively... but what does the other number refer to... the pilot drill size perhaps and if so... what is a no. 10 or no. 8 drill

Below 1/4” you have numbered machine screw sizes and typically fine or coarse threads - like this: Bolt Depot - Threads Per Inch Table for US Bolts

So you can have a #10-24 or #10-32 - a #10 size with 24 or 32 threads per inch. Notice that fine and coarse is dependent upon the size. So you could have a #10-32 which is fine thread (for the size) while a #6-32 is coarse thread (for the size).

Another one of the taps has all of this on a single small tap ( I had to use a magnifying glass to read it) Threadit (the brand I suspect)... 6-32.... Made in USA.... use drill no. 36..... This tap is less than 1/8 in diameter.... What is drill no. 36?... I do realize it is a reference to the pilot drill size but what size is no. 36....

Same as above - a #6 size with 32 threads per inch (coarse thread). And - as you seem to have found - there are letter, number, and fractional drill sizes. To make matters more confusing, the letter and number bits are mixed in between the fractional sizes - number sizes below 1/2” and letter sizes between 1/2” and 7/16”: http://www.smithbearing.com/images/pdf/ENG-FractionalChart.pdf

And no, the number size drill bits don’t correspond in any way to the number sized machine screws - with screws a larger number means a larger diameter while for drill a larger number means a smaller diameter.

 

[half k cruiser]

Why didn't we just switch to the metric system back in the 70's. Life would have been so much easier if we had just given up on doing it this way.

 

[PAToyota]

Politics…

I was in seventh grade when there was the big push for the metric system. Congress passed the Metric Conversion Act of 1975. Even had a class in school. The metrification board was abolished in 1982 by Ronald Reagan.

 

[ferg]

It was a pain. That's how the US got 15mm bolt heads from the auto builders. Dumb.

 

[Dynosoar]

15mm is DIN
It would be awesome to switch over to metric (We would probably go DIN not JIS)

Dyno

 

[ferg]

ok, what is DIN and JIS?

 

[zebrabeefj40]

DIN is a German standard for metric bolt dimensions. JIS is a Japanese standard for bolt dimensions. Here in the USA we also use SAE plus DIN and JIS. Great for tool companies - PITA for the mechanic...

Nick